Influence of Ion Diffusion on the Lithium-Oxygen Electrochemical Process and Battery Application Using Carbon Nanotubes-Graphene Substrate

Ionogel-Based Electrodes for Non-Flammable High-Temperature Operating Electrochemical Double-Layer Capacitors

The design of interfaces between nanostructured electrodes and advanced electrolytes is critical for realizing advanced electrochemical double-layer capacitors (EDLCs) that combine high charge-storage capacity, high-rate capability, and enhanced safety. Toward this goal, this work presents a novel and sustainable approach for fabricating ionogel-based electrodes using a renewed slurry casting method, in which the solvent is replaced by the ionic liquid (IL), namely 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI). This method avoids time-consuming and costly electrolyte-filling steps by integrating the IL directly into the electrode during slurry preparation, while improving the rate capability of EDLCs based on pure non-flammable ILs. The resulting ionogel electrodes demonstrate exceptional electrolyte accessibility and enable the production of symmetric EDLCs with high energy density (over 30 Wh kg-1 based on electrode material weight) and high-rate performance. These EDLCs could operate at temperatures up to 180 °C, far exceeding the limitations of traditional EDLCs based on organic electrolytes (e. g., 1 M TEABF4 in acetonitrile, up to 65 °C). Ionogel-type EDLCs exhibit remarkable long-term stability, retaining 88 % specific capacity after 10000 galvanostatic charge/discharge cycles at 10 A g-1 and demonstrating superior retention compared to conventional EDLCs (50 %), while also maintaining 92.4 % energy density during 100 h floating tests at 2.7 V. These electrochemical properties highlight their potential for robust performance under demanding conditions. This study highpoints the practical potential of ionogel-based electrodes to advance IL-based EDLC technology, paving the way for next-generation energy storage devices with high-temperature and high-voltage operational capabilities.

Hydrogen-Assisted Thermal Treatment of Electrode Materials for Electrochemical Double-Layer Capacitors

The capacitance of electrode materials used in electrochemical double-layer capacitors (EDLCs) is currently limited by several factors, including inaccessible isolated micropores in high-surface area carbons, the finite density of states resulting in a quantum capacitance in series to Helmholtz double-layer capacitance, and the presence of surface impurities, such as functional groups and adsorbed species. To unlock the full potential of EDLC active materials and corresponding electrodes, several post-production treatments are commonly proposed to improve their capacitance and, thus, the energy density of the corresponding devices. In this work, we report a systematic study of the effect of a prototypical treatment, namely H2-assisted thermal treatment, on the chemical, structural, and thermal properties of activated carbon and corresponding electrodes. By combining multiple characterization techniques, we clarify the actual origins of the improvement of the performance (e.g., > +35% energy density for the investigated power densities in the 0.5-45 kW kg-1 range) of the EDLCs based on treated electrodes compared to the case based on the pristine electrodes. Contrary to previous works supporting a questionable graphitization of the activated carbon at temperatures <1000 °C, we found that a "surface graphitization" of the activated carbon, detected by spectroscopic analysis, is mainly associated with the desorption of surface contaminants. The elimination of surface impurities, including adsorbed species, improves the surface capacitance of the activated carbon (CsurfAC) by +37.1 and +36.3% at specific currents of 1 and 10 A g-1, respectively. Despite the presence of slight densification of the activated carbon upon the thermal treatment, the latter still improves the cell gravimetric capacitance normalized on the mass of the activated carbon only (CgAC), e.g., + 28% at 1 A g-1. Besides, our holistic approach identifies the change in the active material and binder contents as a concomitant cause of the increase of cell gravimetric capacitance (Cg), accounting for the mass of all of the electrode materials measured for treated electrodes compared to pristine ones. Overall, this study provides new insights into the relationship between the modifications of the electrode materials induced by H2-assisted thermal treatments and the performance of the resulting EDLCs.